This invention relates to land mine detectors, and more particularly, to circuitry for enhancing the detection of non-metallic as well as metallic land mines.
The development and deployment of metallic land mines was followed by the development of detector systems for locating these buried metallic land mines. Most of these mine detector systems operated satisfactorily until non-metallic land mines were developed. Generally the prior art metallic land mine detectors either will not detect a buried non-metallic land mine or will not detect such a non-metallic land mine with a high degree of reliability. Thus, new detector systems capable of detecting both metallic and non-metallic land mines had to be developed. Several systems for detecting both metallic and non-metallic land mines have been developed and are presently being used. In one such prior art system that is presently being used, the signals from the search head are applied to processing circuitry in which the signals from the search head are chopped at a 1KHz rate, then amplified and low pass filtered to obtain a DC signal comparable to the signal from the search head. This DC signal is applied to an amplitude sensitive gate which controls the gain of a second amplifier. If the signals from the search head are of sufficient amplitude, the second amplifier provides an output signal indicating that a mine has been traversed by the search head.
While the prior art system detects the presence of buried non-metallic and metallic land mines, this system suffers from the fact that varous types of backgrounds can produce signals of sufficient amplitude to produce the same output produced by a land mine. This creates a situation where many signals other than true signals indicate the presence of a buried mine. The operation of this search system has no way of knowing if a given signal is a false or true signal; therefore neutralization steps must be taken eventhough no mine is present. This generation of false signals increases greatly the sweep time required to traverse a given area and causes loss of operator confidence.
This invention solves the problem of false signals by examining in addition to amplitude, the pulse width and slope of the signals from the search head. If a signal from the search head meets the slope, pulse width and amplitude requirements established by the circuitry of this invention, that signal qualifies as a mine signal and an output signal indicating the presence of a mine is produced. By examining these three parameters of the signals from a search head instead of just amplitude, this invention enhances mine signal detection while rejecting spurious signals.